1. Field of the Invention
The present invention relates to an inkjet recording apparatus, in particular, using a so-called fill-before-fire method for ink ejection.
2. Description of Related Art
An inkjet recording apparatus that ejects ink by an inkjet system has the following construction. The inkjet recording apparatus includes therein an inkjet head on which nozzles are formed for ejecting ink. Ink is supplied to the respective nozzles from a common ink chamber formed in the inkjet head. For this purpose, individual ink passages leading from the common ink chamber to the respective nozzles are formed in the inkjet head. For each individual ink passage, an actuator is provided in the inkjet head for applying a pressure to ink in the individual ink passage. Part of ink to which the pressure has been applied by deformation of the actuator is ejected from the corresponding nozzle.
At that time, a pressure wave is generated by applying the pressure to ink in the pressure chamber, and as a result, proper oscillation is generated in the individual ink passage due to the pressure wave. Japanese Patent Unexamined Publication No. 2003-305852 discloses an inkjet head that efficiently ejects ink by using peaks of such proper oscillation. The inkjet head of the publication adopts a so-called fill-before-fire method in which the volume of each pressure chamber is once increased and then the pressure chamber is restored to its original volume after a predetermined time elapses, to apply a pressure to ink in the pressure chamber.
Deformations of such actuators involve various kinds of variations such as manufacturing variations. For example, a case will be discussed wherein an actuator is deformed by supplying a voltage signal to the actuator. In this case, when a voltage signal having therein a difference in voltage is supplied, all actuators are not deformed exactly as designed to correspond to the difference in voltage. As a result, the degree of deformation of an actuator may be a little shifted from its designed value. This causes a shift of the ejection speed of ink from the designed ejection speed when the ink is ejected from the corresponding nozzle by the deformation of the actuator.
When ink is ejected from an inkjet head using a fill-before-fire method as disclosed in the above publication, some shapes of individual ink passages may cause a too large shift of the ink ejection speed relative to the shift of the degree of deformation of the corresponding actuator When the ink ejection speeds are thus largely shifted relatively to the shifts of the respective actuators, the ink ejection speed widely varies from actuator to actuator or from ink ejection to ink ejection. When the ink ejection speeds are largely shifted, variation in ink ejection speed is wide relatively to variation in the degree of actuator deformation. This may cause a reduction of the reproducibility of an image to be formed on a printing paper.